Aromatic polycarbonate, further referred to herein as polycarbonate, is a widely used raw material in many different manufacturing sectors. Due to the hardness and transparency of the material, it can be applied in applications as diverse as automotive windows and optical lenses. It is believed that the demand for polycarbonate will increase significantly in the coming years, requiring improvements in the production of polycarbonate, particularly in terms of efficiency and environmental impact.
Several processes for the production of polycarbonate are known. For instance, a process including reacting phosgene and 2,2-bis(4-hydroxyphenyl)propane (BPA) under phase transfer conditions is applied on an industrial scale. However, this process has the inherent drawbacks of employing the toxic component phosgene and creating chloride containing waste streams.
A different process that does not require the use of phosgene is based on the transesterification of BPA with dialkyl carbonate or diaryl carbonate. The use of a dialkyl carbonate has the disadvantage that in the transesterification with bisphenolacetone, it is not reactive enough under commercially reasonable conditions, to form sufficient quantities of polymeric polycarbonate. Furthermore, the alkyl alcohol that is liberated is not used in any other part of the process for producing polycarbonate, and recycling of the alkyl alcohol to the dialkyl carbonate production requires substantial purification.
The use of a diaryl carbonate, in particular diphenyl carbonate (DPC), has the advantage that it is reactive enough to form polymeric polycarbonate. Furthermore, phenol is liberated in the reaction of the diphenyl carbonate with bisphenolacetone to form polycarbonate, for instance as described in U.S. Pat. No. 5,589,564. This phenol may in turn be recycled to the production of bisphenolacetone or diphenyl carbonate, for which it is a main raw material. Diphenyl carbonate is expensive and it is desirable to find a way to carry out this process without the substantial cost of using large amounts of diphenyl carbonate. The above process for production of polycarbonate leaves ample room for improvement, in particular in view of the raw materials that are used.
JP S64-16826 describes a process for producing polycarbonate comprising three steps. In the first step, bisphenol acetone is reacted with a dialkyl carbonate at a ratio in the range of 1:1 to 1:100. This reaction produces a dialkyl biscarbonate of bisphenol acetone which is then reacted with an equimolar or greater amount of diphenyl carbonate to produce polycarbonate. In the third step, alkyl phenyl carbonate produced as a byproduct is converted to diphenyl carbonate and dialkyl carbonate.